1. Field of the Invention.
The present invention relates to a mechanism for adjusting the clearance between a valve and a valve actuator in a small internal combustion engine of the type which are used in lawn mowers, lawn and garden tractors, sport vehicles, and other small implements.
2. Description of the Related Art.
Small internal combustion engines, such as single or two cylinder engines, include at least one intake and at least one exhaust valve per cylinder, the intake valve openable to allow an air/fuel mixture into the combustion chamber of the cylinder for combustion, and the exhaust valve openable to allow venting of exhaust from the combustion chamber after combustion. In a side valve or L-head engine, the intake and exhaust valves are typically actuated by respective lifters driven by rotating cam lobes. In an overhead valve (OHV) engine, the intake and exhaust valves are typically actuated by rocker arms connected to push rods, which in turn are actuated by lifters. In an overhead cam (OHC) engine, the intake and exhaust valves are typically directly actuated by the cam lobes of an overhead camshaft.
Regardless of the type of valve train in the engine, a small clearance space, sometimes referred to as valve lash, is desired between the end of the stem of each valve and its respective valve actuator in order to ensure that the valve is fully closed or seated at all times when the valve is not being specifically actuated for opening. If such clearance is not present, the valve may be opened or unseated slightly during the period in which the valve should normally be fully closed, thereby disrupting the internal combustion process and inhibiting engine performance.
Adjustment to achieve the proper clearance between valves and their respective actuators is typically performed during the initial construction of the engine, but may also be performed in some engines as necessary over the useful life of the engine. For example, in a side valve engine, the valve clearance is typically initially set during construction of the engines by selecting valve stems of suitable lengths. In this manner, if the valve clearance is determined by measurement to be improper, such as by measuring with a known xe2x80x9cfeelerxe2x80x9d type gauge, a valve of a length suitable to provide the desired clearance is substituted for the valve initially installed, and the foregoing process is repeated until the desired valve clearance is achieved. In most overhead valve engines, valve clearance may be adjusted during construction of the engine, or any time thereafter, by rotating an adjustment nut at the end of the valve stem, which modifies the point of connection between the valve stem and its associated rocker arm.
What is needed is a valve clearance adjustment mechanism, particularly for side valve engines, which is an improvement over the foregoing.
The present invention provides a valve clearance adjustment mechanism for use in small internal combustion engines such as, for example, side valve engines which generally include intake and exhaust valves actuated by lifters pivotally mounted within the engine housing, which in turn are actuated by cam lobes driven in timed rotation with the crank shaft. An adjustment member is provided for mounting each lifter to a shaft, wherein the adjustment member is eccentric relative to the shaft, such that rotation of the adjustment member modifies the position of the lifter and in turn modifies the valve clearance between the lifter and the valve. After the valve clearance has been properly set, the adjustment member is fixed in position.
The adjustment members are mounted upon shafts attached to the cylinder block in an exemplary side valve engine. The adjustment members include eccentric boss portions mounted on the shafts, the boss portions in turn received within apertures of the lifters to thereby pivotally mount the lifters. The boss portions of the adjustment members are eccentric with respect to the shafts, such that rotation of each adjustment member in a first direction causes corresponding movement of the lifter which reduces the clearance between the lifter and the valve, and rotation of the adjustment member in an opposite direction causes corresponding movement of the lifter which increases the clearance between the lifter and the valve. In this manner, the adjustment member may be rotated as necessary until a proper clearance between the lifter and the valve is obtained, whereupon the position of the adjustment member may be fixed to set the proper valve clearance.
Advantageously, the present valve clearance adjustment mechanism may be used in side valve engines, for example, to adjust and set the valve clearance between the lifters and the valves, thereby obviating the need to replace individual parts in the valve train during initial assembly of the engine in order to set the proper valve clearance.
In one form thereof, the present invention provides an internal combustion engine, including an engine housing; a valve train disposed within the engine housing, the valve train including at least one valve moveable between closed and open positions, and at least one cam lobe mounted for rotation; a shaft supported by the engine housing and moveable between first and second adjustment positions; an adjustment member mounted to the shaft, the adjustment member having an eccentric portion; at least one valve actuator pivotally mounted upon the eccentric portion of the adjustment member, the valve actuator having a first portion in engagement with the cam lobe and a second portion located adjacent the valve to define a clearance space therebetween when the valve is in the closed position, wherein when the shaft is in the first adjustment position, the adjustment member may be rotated to move the valve actuator and vary the clearance space, and when the shaft is in the second adjustment position, the position of the adjustment member is fixed.
In another form thereof, the present invention provides an internal combustion engine, including an engine housing including therein at least one rotatable cam lobe, at least one valve, and at least one valve actuator periodically engaging the cam lobe to actuate the valve, wherein a clearance space is defined between the valve actuator and the valve when the lifter is not engaged by the cam lobe; and a mechanism for adjusting the clearance space, including a shaft having a head portion, the shaft adjustably securable to the engine housing between first and second positions; and an adjustment member mounted to the shaft, the adjustment member having an eccentric portion upon which the valve actuator is pivotally mounted, wherein when the shaft is in the first adjustment position, the adjustment member may be rotated upon the shaft to move the valve actuator and vary the clearance space, and when the shaft is in the second adjustment position, the adjustment member is captured between the shaft head portion and the engine housing to fix the position of the adjustment member.
In another form thereof, the present invention provides the combination of an internal combustion engine including a cam having a lobe periodically engaging a valve actuator to actuate a valve within a housing of the engine, wherein a clearance space exists between the valve actuator and the valve when the valve actuator is out of engagement with the lobe; and a valve clearance adjustment mechanism, including an eccentric adjustment member upon which the valve actuator is pivotably mounted, the adjustment member adjustable to vary the location of the valve actuator and the clearance space; and a shaft upon which the adjustment member is rotatably mounted, the shaft engageable with the engine housing to fix the rotational position of the adjustment member and thereby set the clearance space.
In a further form thereof, the present invention provides an internal combustion engine, including a cam having a lobe periodically engaging a valve actuator to actuate a valve within a housing of the engine, wherein a clearance space exists between the valve actuator and the valve when the valve actuator is out of engagement with the lobe; and a valve clearance adjustment mechanism, including a shaft supported by the engine housing; an eccentric adjustment member rotatably mounted upon the shaft and adjustably supporting the valve actuator, the adjustment member including at least one stop portion engageable with the engine housing to limit the rotation of the adjustment member such that corresponding adjustment of the valve actuator is substantially confined to movement of the valve actuator in a direction parallel to the valve.
In still further form thereof, the present invention provides a method of adjusting the clearance between a valve and a valve actuator which is pivotally mounted upon a shaft within the housing of an internal combustion engine, including the steps of adjusting an eccentric adjustment member disposed between the shaft and the valve actuator to move the valve actuator in one of a direction closer or further away from the valve to provide a desired clearance between the valve actuator and the valve; and rotating the shaft to engage the shaft with the engine housing and capturing the adjustment member in a fixed position between the shaft and the engine housing to fix the clearance between the valve and the valve actuator.